This invention relates to pumps and more particularly to gas-operated liquid pumps such as for example pumps of the type referred to as well water purge pumps.
One class of pumps includes a tubular pump housing, a liquid inlet, a standpipe and an air conduit. The pump housing is sealed at two ends except: (1) there is a liquid inlet at one end controlled by a check valve so that liquid may flow into the housing such as from a well but not out of the housing back into the well through the inlet; (2) the standpipe extends downwardly into the housing and there is a check valve in the standpipe; and (3) the air conduit enters the housing. With this arrangement, water flows into the housing through the inlet and then air is pumped into the housing to force the liquid upwardly through the standpipe.
In a prior art pump of this type, air is pumped into the pump housing to force water up through the standpipe to the surface. The user learns when the pump housing is empty of water by the presence of water being pumped from the standpipe followed by air or by the volume of water pumped from the standpipe. When the pump housing is empty, more water is permitted to enter and the cycle repeated until sufficient water has been pumped from the well. For example, in a purging operation of the well, a number of volumes of the well specified by the Environmental Protection Agency is removed.
This prior art pump has a disadvantage in that air separates slugs of water moving up the standpipe to cause waste time as slugs of water are expelled separated by slugs of air.
In another prior art pump of this type, a bladder pump is suspended within the well water purge pump so that, as the well water purge pump operates, water is expelled, passing through the center of the bladder pump. With other valve connections, the bladder pump operates within the casing and inside of the well water purge pump to draw samples after purging. One prior art pump of this type is disclosed in U.S. Pat. No. 4,701,107.
The prior art pumps of this category have some disadvantages in that the central member of the bladder pump complicates the air lift pump and the standpipe is difficult to purge completely.